1. Field of the Invention
The present invention relates to a keyless entry system, and in particular, to a keyless entry system capable of extending a communication distance on the outside of a vehicle.
2. Description of the Related Art
A keyless entry system which can perform vehicle operation, such as locking and unlocking of the doors of the vehicle, through radio communication between an on-vehicle unit mounted in a vehicle and a mobile device carried by a user of the vehicle without using a mechanical key has spread.
Typically, in the keyless entry system, the on-vehicle unit radio-transmits a signal having a frequency (30 kHz to 300 kHz) in a low frequency (LF) band to the mobile device, and the mobile device radio-transmits a signal having a frequency (300 MHz to 3 GHz) in an ultrahigh frequency (UHF) band to the on-vehicle unit corresponding to the signal having a frequency in the LF band, whereby radio communication is performed between the on-vehicle unit and the mobile device.
In the keyless entry system, on-vehicle equipment, such as a door locking device, is controlled through radio communication between the on-vehicle unit and the mobile device, whereby vehicle operation, such as locking and unlocking of the doors of the vehicle, can be performed. Unlocking of the doors of the vehicle is automatically performed when the user carries the mobile device and approaches the vicinity of the doors of the vehicle. Locking of the doors of the vehicle is automatically performed when the user carries the mobile device and moves away from the vicinity of the doors of the vehicle.
As the keyless entry system, a smart keyless entry system 100 (keyless entry system) described in Japanese Unexamined Patent Application Publication No. 2009-19439, a smart entry system 200 (keyless entry system) described in Japanese Unexamined Patent Application Publication No. 2003-269023, or the like has been suggested. FIG. 7 is an explanatory view showing the configuration of the smart keyless entry system 100 described in Japanese Unexamined Patent Application Publication No. 2009-19439. FIG. 8 is an explanatory view showing the configuration of the smart entry system 200 described in Japanese Unexamined Patent Application Publication No. 2003-269023.
As shown in FIG. 7, the smart keyless entry system 100 described in Japanese Unexamined Patent Application Publication No. 2009-19439 includes an on-vehicle device 110 (on-vehicle unit) which is mounted in a vehicle 130, and a mobile device 120 which is carried by a passenger.
The on-vehicle device 110 has a plurality of LF transmission antennas 112a to 112e for radio-transmitting a signal to the mobile device 120, a UHF receiver 114 which receives a signal radio-transmitted from the mobile device 120, a control device (not shown) which causes a plurality of LF transmission antennas 112a to 112e to radio-transmit various signals and controls on-vehicle equipment based on the signal received by the UHF receiver 114, and an alarm device 154 which gives an alarm when there is an abnormality.
The LF transmission antenna 112a is arranged in the vehicle interior of a front passenger seat side door 134, the LF transmission antenna 112b is arranged in the vehicle interior of a rear door 136, the LF transmission antenna 112c is arranged in the vehicle interior of a driver seat side door 138, the LF transmission antenna 112d is arranged on the front side of the front passenger seat, and the LF transmission antenna 112e is arranged below a vehicle interior rear seat 140. Each of the LF transmission antennas 112a to 112e forms a magnetic field therearound and radio-transmits a signal to the mobile device 120 using the formed magnetic field.
The mobile device 120 has a lock switch 124a and an unlock switch 124b for instructing locking and unlocking of the doors of the vehicle 130. Though not shown, the mobile device 120 has a reception magnetic field detection circuit which receives a signal having a frequency in an LF band radio-transmitted from the on-vehicle device 110, a UHF transmission circuit which radio-transmits a signal having a frequency in a UHF band to the on-vehicle device 110 through a UHF transmission antenna, and a control device which controls the UHF transmission circuit.
In the smart keyless entry system 100, a signal having a frequency in an LF band is radio-transmitted from the on-vehicle device 110 to the mobile device 120, and a signal having a frequency in a UHF signal is radio-transmitted from the mobile device 120 to the on-vehicle device 110, whereby radio communication is performed between the on-vehicle device 110 and the mobile device 120, and on-vehicle equipment mounted in the vehicle 130 is controlled through radio communication between the on-vehicle device 110 and the mobile device 120.
As shown in FIG. 8, the smart entry system 200 described in Japanese Unexamined Patent Application Publication No. 2003-269023 includes an on-vehicle device 220 (on-vehicle unit) which is mounted in a vehicle 201, and a mobile device 210 which is carried by a user.
The on-vehicle device 220 has a control unit 221, a door knob antenna 222, a trunk antenna 223, a vehicle interior antenna 224, and an automatic locking distance switch 230. The control unit 221 controls various on-vehicle devices. The automatic locking distance switch 230 is a switch for designating the length of the automatic locking distance.
The door knob antenna 222 is provided in the door knob of a door of the vehicle 201, the trunk antenna 223 is provided in the knob of a trunk of the vehicle 201, and the vehicle interior antenna 224 is provided at a predetermined position in the vehicle interior. Each of the door knob antenna 222, the trunk antenna 223, and the vehicle interior antenna 224 forms a magnetic field therearound and radio-transmits a signal having a frequency in an LF band to the mobile device 210 using the formed magnetic field.
Though not shown, the mobile device 210 has UHF transmission means for radio-transmitting a signal having a frequency in a UHF band to the on-vehicle device 220, LF reception means for receiving the signal having a frequency in the LF band radio-transmitted from the on-vehicle device 220, a switch for instructing locking and unlocking of the doors of the vehicle 201, and a control circuit which controls the entire mobile device 210.
In the smart entry system 200, a signal having a frequency in an LF band is radio-transmitted from the on-vehicle device 220 to the mobile device 210, and a signal having a frequency in a UHF band is radio-transmitted from the mobile device 210 to the on-vehicle device 220, whereby radio communication is performed between the on-vehicle device 220 and the mobile device 210, and on-vehicle equipment mounted in the vehicle 201 is controlled through radio communication between the on-vehicle device 220 and the mobile device 210.